The Taliban's recent release of Sgt. Bowe Bergdahl has prompted a firestorm of political debate. Bergdahl was captured by the Taliban after he wandered away from his unit in Afghanistan. Some have rushed to brand him a deserter and a traitor. Other,s including his friends and family, have rushed to his defense. Today we step away from that debate to look at what we've learned about the psychological effects of being captured in wartime. We've asked NPR social science correspondent Shankar Vedantam, who joins us regularly on this program, to take a deep dive into six decades of research into the lives of prisoners of war. Shankar, welcome.

SHANKAR VEDANTAM, BYLINE: Good morning, Linda.

WERTHEIMER: So what did you find?

VEDANTAM: Well, there has been a staggering amount of research into the minds of prisoners of war. Now, much of this research is actually quite old and looks at U.S. POWs from the World War II and the Vietnam War. And that's partly because after World War II, for example, there were about 143,000 American prisoners of war. By contrast, the United States has had far fewer POWs in recent conflicts. There's also a lot of work from other countries that have had even more experience dealing with returning POWs. After World War II, for example, the number of German and Japanese POWs numbered in the millions.

WERTHEIMER: So are there some kind of patterns that emerge from all that work?

VEDANTAM: Yes, there are patterns, Linda, and some of the patterns in some ways match our intuition. So the conditions of capture seem to matter enormously. German POWs captured by the Soviet Union, for example, were treated much more harshly than POWs that were captured by the Americans and British. They were also held for much longer, sometimes for years and years after the war.

Patricia Sokur (Ph) and other scholars find that torture obviously has negative consequences. They also find that POWs who were younger when they were captured seem to have worse outcomes than POWs who were older. Soldiers who are more junior in rank also seem to be affected worse.

Malnutrition plays a very big role in the long-term psychological effects of POWs. In one analysis of American POWs after the Vietnam War, Francine Segovia and her colleagues found that having an optimistic outlook was protective in terms of the psychological effects of capture. So mental makeup, mental preparedness, maturity, seniority - all seem to make a difference. But broadly researchers have long talked about the three Ds that affect your mind when you're captured during war - debility, dependency and dread.

WERTHEIMER: Well, I suppose that makes sense. To be a POW might involve dealing with illness without proper medical attention. You're obviously dependent upon others of what happens to you, and you must be costly afraid of what might happen to you.

VEDANTAM: That's exactly right. It also seems to matter what the conditions are when you returned home. Are you coming home to a country that's a functioning country, or are you coming home to a country that's wrecked by war? There's another question - are you welcomed back when you come home? Are you treated well? German soldiers who return to Germany after World War II and some American serviceman after the Vietnam War were often at the receiving end of hostility from a larger nation. Obviously your long-term mental outcomes are going to be worse when you're not welcomed back with open arms.

WERTHEIMER: So is there research on what can be done to help these people?

VEDANTAM: There's been a lot of work on that. Post-traumatic stress seems to be an enduring problem. There was an Israeli study by Zahava Solomon and Rachel Dekel that found that among returning POWs, they tended to be emotionally withdrawn. And this created marital problems, and it created these vicious cycles of persistent loneliness.

Now, there's not necessarily a one-size-fits-all treatment because obviously the experience of someone being a prisoner of war intersects with larger conditions and the prisoners own pre-existing mental health conditions. It's also worth pointing out, Linda, that the effects of the POW experience are not uniformly negative. There was a study by Christopher Erbs (ph) and his colleagues looking at World War II and Korean POWs in the Minnesota and Wisconsin area. And he found that at least some of these men reported the experience increased their sense of resilience, and some of them realize that they were tougher than they thought they were.

WERTHEIMER: Thanks, Shankar.

VEDANTAM: Thank you, Linda.

WERTHEIMER: That's Shankar Vedantam who regularly joins us to talk about social science research. You can follow him on Twitter at @HiddenBrain. You can also follow this program at @MorningEdition.